1) Field of the Invention
This invention relates to a pad for an air bag device, said pad normally covering and storing an air bag which is to be inflated under a predetermined situation to protect an occupant of an automotive vehicle or the like.
2) Description of the Related Art
As an impact-reducing device for supporting a seat belt system provided to safely restrain an occupant or a vehicle or the like in a seat, air bag devices have been put into practical use in recent years. According to these air bag devices, the occupant's body, especially his head and chest, are supported by a balloon-like air bag in the event of a collision, followed by the gradual release of the internal gas, so that the impact-reducing stroke can be prolonged to lower an impact to be applied to the occupant's body.
Such an air bag device comprises a folded air bag and an inflator (gas generator), for example, both stored inside a center pad of a steering wheel. The inflator is ignited by an electrical signal from a sensor which detects a collision of the vehicle, whereby the air bag is instantaneously caused to expand by combustion gas so ignited. A top wall of the center bad must therefore be severed and opened by the expanding pressure of the air bag, so that the air bag can be inflated out through the severed opening to a substantial extent above the center pad.
As is disclosed in Japanese Patent Application Laid-Open (Kokai) Nos. SHO 50-127336, SHO 55-110643 and HEI 1-204838 and Japanese Utility Model Application Laid-Open (Kokai) Nos. SHO 63-155869, SHO 63-192159, SHO 63-251353, SHO 64-42959 and HEI 1-123566, a pad of the above sort is formed of a soft synthetic resin such as a polyurethane so that, when its associated air bag expands, it can be severed by the expanding pressure. In addition, it has a severable, thin-walled portion, for example, having a substantially H shape as viewed from the top so that a top wall of the pad can be severed into sections of the substantially the same size.
Moreover, it is desirable to make the top wall of the thin-walled portion as thin as possible so that the top wall can be easily severed into sections of the substantially the same size upon expansion of the air bag. The thickness of the thin-walled portion is therefore set at approximately 1.0-0.5 mm as opposed to a thickness of about 4.0-7.0 mm for the thickness of the remaining portion.
Further, to prevent the pad of the above type from being broken up into small pieces and spreading around upon inflation of the air bag, a net-like insert made of flexible, synthetic fibers such as polyamide fibers is embedded.
When a pad with such a net-like insert embedded therein is formed by injection molding, it is difficult and cumbersome to set the net-like insert inside a mold because the net-like insert is made of a flexible material. Further, when a pad having a thin-walled portion is formed by injection molding, short molding tends to occur at the thin-walled portion. This has led to the problem that a high percentage of products molded as described above are defective and the productivity of such pads is not good.
Formation of the thin-walled portion in an unduly small thickness however results in the potential problem that the pad may be severed when the air bag is not inflated, namely, when its severing is not needed, for example, when the pad is pressed by a hand or the like.